An exemplary prior art hardware/software display arrangement in a computer system is shown in FIG. 1. A display memory 102 is connected to display circuitry 104, which generates a display signal based on the contents of display memory 102. Display memory 102 contains data representing display windows controlled by various application programs, such as owning application window 106 and other application windows 108.
Also present in the computer system is main memory 10, which contains a variety of programs and routines that are executed by the computer system. Main memory contains owning application 112, other applications 114, display management application program interfaces (API's) 116, device drivers 118 and, in this example, requesting application 120. Although the term application is used in this document to refer to application 112 and other applications 114, one of skill in the art would recognize that the description herein is equally applicable to any executing process in a computer system.
Owning application 112 owns owning application window 106, while the other applications 114 own the other application windows 108. Owning application 112 may display data of any kind, such as text, images, video, etc., in owning application window 106, as well as other objects, such as control buttons, text entry boxes, sliders, etc. For example, owning application 112 may display data such as displayable data 115. In order to display data or other objects, owning application 112 communicates with display memory 102 through APIs 116, which provide a device-independent interface to the device-specific device drivers 118, which access and control the hardware of display memory 102 and display circuitry 104.
Another application, such as requesting application 120 may request access to the data displayed in application window 106. A problem arises when the requested data is unobtainable, such as may occur when the data is protected from access, when the data is in a format that is not compatible with the data request, or when the data simply does not exist, as may occur if a window is not actually visible. Currently, an error is generated and no data is returned.
A need arises for a technique that will determine what data should be supplied to an application when the application attempts to access data that is either not present, or not authorized to be accessed.